Electric lamp



April 30, 1940' G. F. PRIDEAUX ELECTRIC LAMP Filed latch 21. 1939 Inventor I Gwilgrh F. Prideaux,

His Attorneg.

Patented Apr. 30, 1940- PATENT OFFICE ELECTRIC LAMI' Gwilym F. Prideaux, Cleveland Heights, Ohio, as-

signor to General Electric Company, a corpora-- tion of New York Application March 21, 1939, Serial No. 263,176 4 Claims. (01.176-16) My invention relates in general to electric incandescent lamps comprising a glass bulb having an electrical energy translation element sealed therein and a base secured thereto. More specifically, my invention relates to mount constructions for such lamps, and in particular to mount constructions for miniature lamps of the butt-sealed type.

In many types of electric incandescent lamps as manufactured at present, a coiled filament of, ductile tungsten or other suitable refractory metal is supported within a glass bulb between two substantially parallel leading-in wires which are sealed into the glass of thebulb at a point considerably removed from the filament. Thus in miniature lamps of the butt-seal type, a small coiled filament is supported by a mount structure comprising two substantially parallel leading-in wires sealed into the bulb wall at the base end thereof and extending into the bulb, the filament being connected to the inner ends of the leadingin wires and a bead of insulating material tying the two leading-in wires together in spaced relationship at a point intermediate their inner ends and the point of sealing-in. At present, these mount structures are of such construction that when the lighted lamp is subjected to a blow or shock or to vibrations at certain frequencies, the filament vibrates at a different frequency and at a different amplitude than that of the filament engaging ends of the leading-in wires. A particularly bad condition occurs when the natural frequency of the leading-in wires is the second harmonic of the filament vibration frequency. A frequent result, particularly with repeated shock, is that the ductile tungsten coil of the hot filament becomes distorted, adjacent turns or even large sections of the coil are short circuited, and early burn-out of the filament oco curs. In some cases the filament may even fracture. The destructive effect of the above referred to filament vibration is particularly troublesome in the case of radio panel lamps, which are subjected to considerable vibration, during operation of the radio, as a result of the sound vibrations produced thereby.

I have discovered that by making the filament support of the proper degree of flexibility, and by designing the same so that it will have ap- 50 proximately the same fundamental frequency at its inner or filament-engaging ends as the filament, the resistance of the filament to failure resulting from physical shock is materially increased, in some cases as much as ten-fold. With 5 such a. construction the filament will not violently vibrate independently of the support wire ends and so become distorted.

One object of my invention is to provide an electric incandescent lamp which will withstand a. considerable amount of physical shock before failure of the filament thereof.

Another object of my invention is to provide an improved mount construction for electric incandescent lamps which will minimize distortion of the filament when the lamp is subjected to physical shock.

Still another object of my invention is to provide a lamp filament support structure having approximately the same fundamental frequency at its filament engaging points as that of the filament itself.

A further object of my invention is to provide a lamp filament support structure having approximately the same fundamental frequency and the same degree of flexure at its filamentengaging points as that of the central portions of the filament itself.

Further objects and advantages of my invention will appear from the following description of a species thereof and from the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view on an enlarged scale of a miniature lamp provided with a mount construction "comprising my invention;

Fig. 2 is a side elevation on an enlarged scale of the mount structure shown in Fig. 1 illustrating the manner in which the mount vibrates when subjected to physical shock; and Fig. 3 is a top view of the mount structure shown in Fig. 1 likewise illustrating the manner in which the mount vibrates when subjected to physical shock.

Referring to the drawing, the lamp there shown comprises a small cylindrical glass bulb or envelope l0 having a base ll secured thereto, preferably by cement 12. The base ll may be either of the bayonet or screw-thread type, and comprises a substantially cylindrical metal shell l3, insulation I4 and a bottom center contact IS. A coiled or coiled-coil filament I6 of a suitable refractory metal, preferably tungsten, is mounted within the bulb l0 adjacent the tip or outer end thereof by means of a pair of spaced longitudinally extending inner leading-in wires l1, l8.

The said filament is connected to the inner ends of the said leading-in wires in such a manner as to extend substantially transversely of the bulb Ill. The leading-in wires l1, l8 extend through the glass of the bulb at the base end thereof, the said wires being sealed into the glass at this point by the well-known butt seal method.

Lead wire ll extends through an opening I! in the opening IS in the base insulation I where it is secured to the bottom center contact l5, while lead wire I8 is bent back over the edge or rim of the base shell l3 and is secured thereto by means of solder 20. A bead or bridge member 2| of suitable insulating material, preferably glass, surrounds the two leading-in wires l1, It. The said head thus serves to maintain the leading-in wires in spaced relation and to strengthen the mount structure as a whole. I

According to the invention, the lamp mount structure, comprising the inner leads ll, l8 and the bead of insulating material 2|, is so constructed as to have substantially the same fundamental frequency and preferably, in addition, the same degree of flexure at its filament-engaging ends as that of the coiled filament Hi. In the lamp shown in the drawing, this equalization of the respective frequencies of the mount structure and coil filament is efiected by employing longer inner leading-in wires l1, l8 than heretofore, and by locating the head of insulating material 2| at a definite point on the leading-in wires, the said point in general being much closer to the filament than the point at which it has been heretofore customary to mount the bead. Obviously, the point of bead location will depend upon a number of variables, such as the size and weight of the bead and the length, diameter and composition of the inner leading-in wires l1, l8.

Although preferable, it is not necessary that the fundamental vibration frequency of the mount be exactly the same as that of the filament. For the purposes of the invention, it is only necessary to have the respective frequencies of the mount and the filament sufficiently close together to enable the heavier mount structure to force its period of vibration onto the filament, thereby causing the filament to vibrate in unison with the mount structure.

In a specific example of a radio panel lamp embodying the principle of my invention, the leading-in wires were made of "Dumet wire having a diameter of approximately 10 mils, and extended inwardly from the seal a longitudinal distance of approximately 15 mm., this distance representing the stem height of the lamp mount. The filament height, that is, the distance from the seal to the top of the filament, was approximately 16 mm. The filament itself was made from tungsten wire having a weight of approximately 3.26 milligrams per 200 mm. of length, and formed into a coil having 370 turns per inch and an inside diameter of approximately 6.6 mils. The coil width, that is, the straight-line distance between the ends of the coiled portion of the filament, was approximately 3 mm., while the coil height was approximately mm. The filament legs were attached to the leading-in wires at a point approximately mm. from the ends of said wires. The insulating bead H was made of glass and had a height (longitudinally of the lamp) of approximately 1 mm. and a weight of approximately 0.0348 gram. The bead was mounted on the leading-in wires at a distance from the seal of approximately 11 mm., measured to the bottom of the bead.

When a lamp according to the invention is subjected to a physical shock, particularly at right angles to the plane of the filament and leading-in wires, the resulting vibration of the filament and mount structure produces very little, if any, distortion of the filament. Because of the correspondence of the filament and mount vibration frequencies, the filament-engaging ends of the leading-in wires l1, l8 move in unison with the central portions of the filament throughout the entire period of vibration, as shown in Figs. 2 and 3, thus minimizing distortion of the filament. Where the flexibility of the mount structure is, in addition, made such that the amplitude of movement of the leading-in wires, at the point of connection to the filament, approximates that of the central portion of the filament, then there is practically no distortion whatever of the filament. This condition is clearly illustrated in Figs. 2 and 3 in which the distance I, denoting the amplitude of vibration of the central portions of the filament, is substantially equal to the distance I representing the amplitude of vibration of the filament engaging ends of the leading-in wires.

' While in the above description I have disclosed the preferred manner of equalizing the fundamental frequencies of the filament and the mount structure, there are other ways in which the same objective may be accomplished. Thus, the leading-in wires may be reduced in size, flattened in a section, changed in composition, or coiled as a spring near the seal to the glass bulb. Furthermore, while the invention has been described in connection with miniature lamps, it is obvious that it is equally well applicable to certain types of large lamps to thereby prevent appreciable independent, and consequently destructive, vibration of the filament relative to the support or leading-in wires.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric incandescent lamp comprising an envelope, a coiled filament sealed within said envelope, and a resilient support mount for said filament comprising a. pair of leading-in wires extending into said envelope in the same general direction, said mount and said filament having approximately the same fundamental vibration frequency in a direction normal to the plane passing through said leading-in wires so that they vibrate in unison.

2. An electric incandescent lamp comprising an envelope, a coiled filament sealed within said envelope, and a resilient support mount for said filament comprising a pair of leading-in wires extending into said envelope in the same. general direction, said mount and said filament having approximately the same fundamental vibration frequency in a direction normal to the plane passing through said leading-in wires so that they vibrate in unison and the filament engaging points of said mount having approximately the same degree of flexure as that of the central portions of said filament.

3. An electric incandescent lamp comprising a glass envelope, a coiled filament sealed within said envelope, and a resilient support mount for said filament, said support mount comprising a pair of spaced leading-in wires sealed through and extending into said envelope in the same general direction, said filament extending between the inner ends of said leading-in wires and being supported thereby in the plane passing through said leading-in wires, and a bead of insulating material tying the said leading-in wires together at a predetermined distance from their said inner ends, said support mount being so constructed and arranged as to have approximately the same fundamental vibration frequency as that of said filament in a direction normal to the plane passing through said leading-in wires so that said filament and mount vibrate in unison. 4. An electric incandescent lamp comprising a glass envelope, a coiled filament sealed within said envelope, and a resilient support mount for said filament, said support mount comprising a pair of spaced leading-in wires sealed through and extending into said envelope in the same general direction, said filament extending between the inner ends of said leading-in wires and being supported thereby in the plane passing through said leading-in wires, and a bead of insulating material tying the said leading-in wires together at a predetermined distance from their said inner ends, said support mount being so constructed and arranged as to have approximately the same fundamental vibration frequency and the same degree of flexure at the said inner ends as that of the central portions of said filament in a direction normal to the plane passing through said leading-in wires so that said filament and mount vibrate in unison.

GWILYM F. PRIDEAUX. 

